Scuba diving breathing systems include open-circuit and rebreather systems. In open-circuit systems, all of the diver's exhaled air is exhausted to the ambient environment (e.g. typically, into the surrounding water). In rebreather systems, at least a portion of the diver's exhaled air is recaptured and is recycled through a breathing loop which typically includes an expandable/contractible counterlung and a carbon dioxide scrubber. Rebreather systems include one or more gas supplies, containing gas such as pure oxygen, a mixture of oxygen, nitrogen and/or helium (e.g. trimix or nitrox) and/or the like. Gas from the one or more gas supplies is injected into the breathing loop to replenish the air consumed and/or exhaled by the diver.
Rebreather systems may be provided as closed-circuit or semi-closed circuit systems. In closed-circuit systems, all of the diver's exhaled air is recaptured and recycled through the breathing loop. Closed-circuit systems typically supply a combination of pure oxygen and a diluent gas (e.g. air or trimix) to the breathing loop, and include oxygen monitoring systems to monitor and adjust oxygen levels to guard against oxygen toxicity. In semi-closed circuit systems, a portion of the diver's exhaled air is exhausted from the rebreather loop to the ambient environment (typically from a port in the breathing loop located on the diver's back) and the remainder is recaptured and recycled through the breathing loop. Semi-closed circuit systems typically supply gas mixtures (e.g. nitrox) to the breathing loop and do not require oxygen monitoring systems. Semi-closed circuit systems tend to involve fewer components and are generally lighter, more compact, and easier and safer to use and maintain than closed-circuit systems.
In rebreather systems, a diver exhales and inhales through a mouthpiece which directs an incoming supply of air from the breathing loop to the diver's mouth, and directs outgoing or exhaled air from the diver's mouth toward the breathing loop for recirculation through the breathing loop. In semi-closed circuit rebreather systems, a portion of the exhaled air is discharged or exhausted to the ambient environment, typically at an outlet in the breathing loop and away from the mouthpiece.
There is a need for a mouthpiece which may be used with semi-closed circuit rebreather systems. There is a need for a mouthpiece which exhausts a portion of the exhaled air to the ambient environment while directing the remainder of the exhaled air to the breathing loop.